1. Field of the Invention
The present invention relates to a composite control arm shaft for motor vehicles which includes two longitudinal control arms connected through a transverse beam, wherein the transverse beam has a trough-shaped double-wall torsion section essentially having the form of a V or U, approximately circular or oval tubular end sections and transition sections whose cross-section continuously changes from the end sections toward the torsion section.
2. Description of the Related Art
EP 0 229 576 B1 discloses a composite control arm shaft manufactured from a pipe, wherein the wheel-supporting longitudinal control arms extend parallel to each other and are tubular without being deformed. The transverse beam connecting the longitudinal control arms is stiff with respect to bending but soft with respect to torsion and has, except for the tubular ends which are also circular, a cross-section which is L-shaped, V-shaped, T-shaped, U-shaped, X-shaped or H-shaped.
However, the use of a composite control arm shaft of the type described above has in the past posed difficulties in practice because of the demanded service life. In U-shaped and V-shaped transverse beams, the reason for not reaching a satisfactory service life is the high load acting in the transition areas between the deformed and the non-deformed length sections, so that a premature failure occurs in these length sections in the case of a long-term load.
A transverse beam for a composite control arm shaft which is substantially improved over the one described above is disclosed in DE 196 53 959 C1.
In addition, DE 35 11 495 A1 discloses a wheel control arm for motor vehicles which includes a foam core-supported base body. The wheel control arm manufactured of composite fiber material has a base body of hard foam corresponding to the basic shape of the control arm. Reinforcements, such as inner and outer sectional rods and cover plates, are mounted around this base body to produce a dimensionally correct final shape.
Therefore, starting from the prior art discussed above, it is the primary object of the present invention to provide a composite control arm shaft which can be subjected to high loads, wherein the composite control arm shaft is improved with respect to the stiffness and strength behavior and has a longer service life.
In accordance with the present invention, the transverse beam has in the transition sections thereof an internal partial foam filling.
Consequently, at the core of the invention is the measure of providing the transverse beam of the composite control arm shaft in the transition sections from the V-shaped or U-shaped torsion section to the approximately circular or oval tubular end sections with an inner partial foam filling or core.
This measure results in a reinforcement of the composite control arm shaft and an increase of its service life.
The targeted reinforcement or stiffening in the transition sections of the transverse beam from the V-shaped or U-shaped cross-section toward the ends is of a material whose volume to a large extent is composed of hollow spaces (bubbles, pores). This results in an effective increase of the stiffness of the transitions while simultaneously increasing the capacity of absorbing or converting energy. The density of the foam filling or core in the transition sections of the transverse beam can be adapted in a targeted manner to the composite control arm shaft or the type of motor vehicle.
As practical tests have shown, the foam filling results in a higher energy absorption in the case of high loads. This has a particularly positive effect in the case of a crash.
In addition, the composite control arm shaft according to the present invention has an improved frequency behavior with respect to alternating tensile and compressive loads. The total configuration of the composite control arm shaft makes possible section moduli which are adapted to dynamic loads. This is to a great extent influenced by the foam filling or core in the transition areas from the torsion section to the ends of the transverse beam. The partial adhesion resulting from the foam filling facilitates an efficient transfer of the torsion and bending forces from the longitudinal control arms into the transverse beam, wherein the forces are compensated in the torsion section of the transverse beam. As a result, the composite control arm shaft according to the present invention has a particularly good static and dynamic load behavior and reaches a long service life.
The invention further results in a weight optimization and a material reduction of the composite control arm shaft. When the wall thicknesses or cross-sections of the transverse beam are reduced, the inner partial foam filling makes it possible to reduce the weight while the strength of the structural component is identical, and the utilization of the available structural space is optimized.
The internal foam filling in the transition sections additionally makes it unnecessary to use additional gusset plates or similar mechanical constructions between the transverse beam and the longitudinal control arms. This results in a further weight reduction as compared to comparable composite control arm shafts.
In accordance with a feature of the present invention, the foam is a synthetic multicomponent foam. The foam used in practice may be a foam on the basis of a synthetic material, such as epoxy foam, polypropylene foam or polyurethane foam. The foams are either injected into the structural components or are foamed within the structural component itself. It is additionally possible in practice to apply the initial foam material in the form of crystals in the transition sections and to foam the material subsequently with the use of energy. This is usually done by heating.
In accordance with another feature, a metal foam may be used.
The metal foams may be aluminum foam or steel foams.
However, basically other metal foams can also be used, preferably light metal foams, such as magnesium foam. Moreover, a multicomponent foam, such as a foam of aluminum and magnesium can be used. The components of the metal foam can be adapted with respect to their operation to the configuration of the composite control arm shaft and the load behavior thereof.
For manufacturing metal foam, a metal powder or a metal alloy powder with a particle size of preferably xe2x89xa6300 xcexcm is used. This powder is mixed with small quantities of a powder-metallurgical expanding or foaming agent, such as titanium hybrid, with a particle size of xe2x89xa665 xcexcm. The mixture results in a homogenous distribution of the gas-separating expanding or foaming agent in the metal powder. Subsequently, the metal powder mixture is compacted or directly introduced into the transverse beam.
Foaming takes place in the next process step by heating the transverse beam or the transition sections.
In accordance with another feature, stiffening fibers can additionally be embedded in the foam matrix of the foam filling. The fibers may be of synthetic material or of metal. The use of mineral fibers is also conceivable.
The material of the foam filling is inert, i.e., its components are not supposed to attack and corrode the material of the transverse beam or of the composite control arm shaft. It is useful if the foam material is corrosion-inhibiting. This can be achieved by adding suitable additives.
In summary, the composite control arm shaft can be manufactured efficiently and inexpensively. By introducing foam into the transition sections of the transverse beam, a structural composite area with increased stiffness is produced. This improves the dynamic and static load behavior of the composite control arm shaft. In addition, the properties with respect to noise, vibration and strength are improved in the transition sections.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.